Protective device



Patented Dec. 13, 1927.]

enemies H. ;@nexms, or rrzr'rsnunqn, HOUSE ELECTRIC & MANUFACTURING vnnm.

PATENT oFFioa PENNSYLVANIA, ASSIGNOR we I wnsrme- COMPANY, A conronnrxou or rnmrsn,

rnorncrrvia 'nnvrcn.

' Application .flled November 8', 1924. Serial in. 748,606.

My invention relates to -thermal protective I devices and particularly. to thermal'relaysr The object of my invention is to provide .a relatively simple, compact, and easily manufactured thermal relay: that shall operate with a snap action.

In' .practlc' g my invention, .1 prov de a current-conducting, thermally respons1ve element of relatively small heat stora'ge ca pacity," and asecond current-conducting thermally-responsiveelement of greater. heat-storage capacity than the first element and having a portion that serves as a latch for'the first element.

In the single sheet of drawings, Figure 1 is a' diagrammatic view of an electric circuit comprising" the dev ce embodying-my invention,

" liig 2is a diagrammatic view of the c1 rcuit illustrated in Fig. 1, vwith the circuitcontrolling, means in its openposition,

Fig. 3 is a top plan view ofone thermallyresponsive element of'the device embodying my. invention,

and. partially-in section, of the parts illustratedin Fig. 3, Fig. 5 i'sja top plan view of a second, thermally-responsivemember. a Fig. 6 is 'afview, mainly in side elevation but partially in section, otthe device shown in Fig.5, Fig. 71s a view, mainly-inside elgvation," of a device embodying my. invention, a por- Y tionthereof being show-nin section, and

v Fig. 8 is an assembled view, in perspective, of a device embodying my invention.

Referring more particularly to Figs. 3 to 8, inclusive, a thermal relay 11 comprises-a thermally-responsive element 12 that is substantially straight .and comprises rtwo suit- .able metal plates, having dissimilar expansion characteristics, closely. united to form a bimetallic strip. J The member 12v is pro vided with a plur'alityoflongitudinal parallel slots or cuts-13 and.14,-respecti vely, extending inwardly from: its oppositeends in order' to providea relatively long path for electric current traversing the member, whereby the same is heated and one. end thereof is. caused to be moved, ina *inanner well known in the art;

QL-One end of the member 12 is mounted-on Fig.4 is a view,,partially in side elevation .thin materials, while a laterally disposed supporting bar. 15, of electric insulating material, and a second bar 16, of electric insulatlng material, is located upon the opposite surface of the member 12- and is adapted to be clamped thereagainst in order to hold the member 12 securely against the supporting member 15.

a A member 17, of substantially U-shape, and of electric insulating material, is. mounts ed upon the free end of the member 12, and held 1n proper operative position by a plurality of small bolts 01 rivets 18 which e2;- tend intoa metal bar or plate 19 located on one side of the member 17, to constitute a vwearing plate, for 'apurpose to be hereinafter set forth in detail.

One end of asecond'bimetallic element 21,

is, fastened-t0 the other surface of the supporting bar' '15 and comprises a plate that is substantial-l co-extensive with the element 12 but has, In addition thereto, a return-bent portion 22 that extends around the free end of the element 12, substantially as illustrated in Figs. 7 and 8 oi the drawings.

A plurality of pairs of opposite and longitudinally extending slots 23 and 24 are provided in the member 21, as is more particularly illustrated in Fig. 5 of the drawing. ,"lhe return-bent end of the element 21 is provided with a metalwearing plate 25 that is secured to its inner surface, a bar 26, of electrlc-i-nsul'ating material, being interposed .therebetween. A bar 27, of electricinsul'ating material, is located upon the outer surface ofthe end of the portion 22, and a plurality oi rivets 28 serve to clamp the mem bers 22,25, 26 and 27 rigidly together.

As is illustrated more particularly in Fig.8, the element 12 is made of relatively the element 21 is made of somewhat thicker materials.

As it is intended that the two elements 12 and 21 shall be traversed by the same main current, suitable means are, provided for connectingelectrical conductors thereto. A conductor 29 is'e'lectrically connected tothe jfixed end of the outer strip of the element 12,

substantially as illustrated in Fig. 3 of the drawing, as by a suitable bolt or screw 31.

:The opposite end strip o'f'the element 12 is connected to the corre nding stri of the element 21, by a throng -bolt 32. e other and or strip of the element 21 is connected, 5,

thereof. The contact terminal 34 is adapted to normally engage a co-operating and substantially stationary contact member 35, that is mounted on a bar 36 of electric-conducting material, which'extends through a suitable opening in the bar 15.

Referring more particularly to Fig. 1 of the drawings, I have there illustrated an cncrgytranslating device 37 .as comprising a suitable motor. However, such energytranslating device may be a transformer, a generator or la heating coil. A circuit reaker 38 comprises the usual contact-terminals and contact bridging members, an actuating coil 39, a core member 41 and a spring 42. Energy for the energy-translating device 37 is provided through a pair of supply-circuit conductors 29 and 43.. The

elements 12 and 21 are. connected in the main circuit substantially as shown in Figs. 1 and 2 of the drawing.

As long as the current traversing the thernal relay 11 and the energy translating device 37 remains below a predetermined value for a predetermined length of time, the po-' sitions of the parts of the relay 11 will-be substantially that illustrated in Figs. 1 and 8 of the drawing. The 'auxiliarycircuit of the relay 11, controlled by the co-operating contacts 34 and 35, Wlll energize the holding coil 39 of the breaker 38 and the breakerwill remain in its closed position.

If, however, an overload-is carried by the energy-translating device 37, for a longer time than is'permissible, the same current, or

a current having a value in accordance with this main current traverses the elements 12 and 21 and causes heating thereof.

As the element 12 has a lower heat-storage capacity than the element 21, by reason of its being thinner, it will heat up sooner and tend to move outwardly or away from the other thermally-responsive element21. By reason of the hereinbefore described con- 7 struction of the element 21, which constitutes a latch for the free end of-the element 12, the latter element is prevented from movin until-the free end of the element 21 is move longitudinally of the element 12sufiiciently 'to unlatch the free end of the element 12 by disengagement of the wearing plates 25 and 19.

end of the element 12 will. move suddenly or witha snap action, and dlsengagement of the-co-operatlng contacts 34 and 35, which control the auxiliary circuit, will also be effected quickly and with a snap action. The final positions of, the various parts-of the relay 11 and of the circuit are illustrated in Fig. 2 of the drawing, in which the brea ker 38 is shown as being in its open position,

causing an interruption of the circuit through'the' energy-translating device 37, to permit'the same to cool.

The respective elements 12 and 21 of the relay llwill begin to'cool as soon as the flow of current therethrough has been interrupted, and the element 12 will tend'to cool faster than the element 21 by reason of its lower heat-storage capacity.- It will,

therefore, move back to its normal position I sooner thanwill the free or return-bent. end of the element 21. Therefore, when the elemcnt 21 has'cooled suificiently to cause it to return to its original position, the. return bent end will again extend around the free end of the element 12 and latch the same in its normal operative po'sition,with the twocontacts 34 and35 in operative engagement.

' If the circuit breaker 38 be automatic, the

circuit will. be 'again 'clos'ed through the energy-translating device 37, upon reener gization of the coil 39, and operationof the energy-translating, device 37 will again be resumed.

The device embodying'my invention thus rovides athermal'relay-having relatively 'ew parts and being, therefore, simple and easy to manufacture' The device further provides a thermal relay that operates with a snap action and that automatically resets vdtself after a predetermined period of-deenergization. y

Variousmodifications and changes maybe.

made without 'departing from the s irit and scope' of the invention, I desire, t 'erefore, that only such limitations shall be placed thereon'as are imposed by the' prior art.

I claim as my invention: Q 1'. A thermal relay comprising a su ing member, a thermally-responsive e ement having one end supported thereby, a second thermally-responsive element supported b saidmember, substantially co-extensive wit said'first element and having an end portion return-bent around-the outer end of-said. first element to serve as a latch therefor at all1 temperatures below a; predetermined va ue.'

2. 'A. thermal relay comprising a support member of electric-insulating material,

1n a longitudinally-slotted, current-conducting, I,

thermally-responsive element having one end mounted on said'supporting member, asecond longitudinally slotted, currentconducting thermally-responsive element supported by porti ol When such disengagement occurs, the free said member and having its outer end renot 

